A method for generating and receiving a hierarchical structure synchronization signal and a receiving device

Abstract

The present invention proposes a method for generating and receiving a synchronization signal and a receiving device. The synchronization signal is composed of multiple layers of synchronization sequences, and the signal obtained in each layer is generated by performing a Kronecker product in the time domain between the synchronization signal of the previous layer and the synchronization sequence of this layer. By flexibly selecting the number of layers and the sequences of each layer, the PAPR requirements and system synchronization requirements of different communication systems can be adapted. There are two methods for implementing the synchronization sequence at the transmitting end: time domain generation and frequency domain generation. At the receiving end, after performing a de-weighted delayed autocorrelation on each layer of the synchronization signal, and then performing recursive processing on the next layer, a correlation detection result can be obtained. The position of the peak of the normalized correlation detection result indicates the timing synchronization information, and the peak phase indicates the frequency synchronization information.

Description

Technical Field

[0001] The invention belongs to the field of communications, and in particular relates to a method for generating and receiving a synchronization channel and a corresponding device thereof. Background Art

[0002] In the existing communication physical layer system, the method of achieving time and frequency synchronization between the transmitter and the receiver is basically based on the synchronization signal. The synchronization signal is a symbol sequence known to both the transmitter and the receiver of the physical layer system. The synchronization signal can be located at the beginning of the physical frame (commonly seen in broadcast systems, usually called a synchronization signal, preamble), or at a fixed position in the middle of the physical frame. The same synchronization signal only appears once in each physical frame or physical block. With the help of the synchronization signal, the receiver can obtain accurate and reliable frame synchronization, symbol timing synchronization, and frequency synchronization. For coherent receivers, an excellent synchronization signal can also provide the channel information or phase reference required for coherent demodulation.

[0003] Currently, the uses of synchronization signals include:

[0004] (1) Enable the receiving end to quickly detect whether the signal transmitted in the channel is the signal it expects to receive;

[0005] (2) Initial frame synchronization;

[0006] (3) Detect the initial carrier frequency deviation and timing error, and achieve frequency and timing synchronization after compensation;

[0007] (4) Providing basic transmission parameters (such as FFT points, frame type information, etc.) so that the receiving end can perform subsequent receiving processing;

[0008] (5) performing channel estimation or reference phase estimation;

[0009] For good synchronization signal design, the following factors need to be considered:

[0010] (1) Low peak-to-average ratio (PAPR) or cubic metric (CM) characteristics, which facilitates the increase of transmit power;

[0011] (2) Low detection complexity. Usually, delayed autocorrelation has lower complexity than cross-correlation, but the noise term of the autocorrelation will be amplified, affecting the processing gain. It is necessary to design a synchronization sequence structure that uses delayed autocorrelation without losing the signal-to-noise ratio;

[0012] (3) The autocorrelation and cross-correlation characteristics should be good;

[0013] (4) When performing independent or joint detection on the time and frequency dimensions, the estimation error of one dimension cannot be too sensitive to the error of the other dimension.

[0014] (5) Meeting certain networking requirements: If the synchronization sequence can provide multiple access orthogonal characteristics, it can be applied to complex networking applications such as cellular mobile communication systems.

[0015] The synchronization signal in the IEEE 802.11 standard uses the characteristics of multiple repetitions in the time domain, which is conducive to delayed autocorrelation processing and has low complexity, but the signal-to-noise ratio loss is obvious, and it must rely on complex cross-correlation operations to obtain better synchronization performance; the synchronization signal in the LTE standard uses a single structure in the time domain, which has made outstanding optimizations in terms of PAPR reduction, networking convenience, autocorrelation / cross-correlation characteristics, but there is no multiple repetition feature in the time domain, and autocorrelation processing cannot be used, so only highly complex cross-correlation processing can be used. In addition, the optimized synchronization sequence sacrifices the anti-frequency deviation characteristics in order to take into account the networking requirements, and puts forward stringent requirements on the maximum frequency deviation allowed by the system. The DVB_T2 and ATSC3.0 standards propose a synchronization signal design based on the OFDM system, which better optimizes the correlation detection performance and achieves an appropriate compromise in complexity. However, the high PAPR and long sequence length are not conducive to rapid detection. In order to reduce PAPR, satellite broadcasting such as DVB-S2 uses time domain constant modulus design, but is limited by the PAPR re-growth effect of upsampling filtering and shaping filtering, and the final PAPR is significantly improved. The present invention proposes a layered synchronization sequence generation method, which can obtain synchronization signals with different processing gains and different lengths by flexibly configuring the number of layers and the length of each layer subsequence, and can widely match the synchronization requirements of various different systems. The sequence supports time domain and frequency domain generation, and can take into account the restrictions of multi-carrier and single-carrier systems on indicators such as spectrum templates. The weighted multiple repetition characteristics of the sequence itself are conducive to the implementation of delayed autocorrelation reception processing. By reasonably designing the synchronization sequence of the sub-layer, the processing gain of the delayed autocorrelation can be made close to the theoretical maximum value, and there will be no significant signal-to-noise ratio deterioration. The sequences and modulation modes of each sub-layer can be designed independently, and targeted combination configurations can be made according to the PAPR requirements. The present invention proposes a corresponding synchronization sequence receiving method and receiving device, and its de-weighted delayed autocorrelation processing method can obtain more ideal correlation characteristics and synchronization performance than traditional multiple time-repeated synchronization sequences. Summary of the invention

[0016] In order to solve the above problem, the present invention proposes a method for generating and receiving a synchronization signal and a receiving device.

[0017] The English and symbols involved in the present invention are explained as follows:

[0018] DFT: Discrete Fourier Transform

[0019] IDFT: Inverse Discrete Fourier Transform

[0020] OFDM: Orthogonal Frequency Division Multiplexing

[0021] MB-OFDM: Multi-Bandwidth Orthogonal Frequency Division Multiplexing

[0022] BPSK: Binary Frequency Shift Keying

[0023] s: hierarchical synchronization signal according to the present invention

[0024] x m : The mth layer subsequence of the layered synchronization signal of the present invention

[0025] L: length of the hierarchical synchronization signal according to the present invention

[0026] M: the number of layers of the hierarchical synchronization signal described in the present invention

[0027] L m :sequence x m Length

[0028] y m : The mth layer output result of the hierarchical synchronization signal of the present invention

[0029] L (m) :y m Length

[0030] N DFT :DFT points

[0031] L cp : Cyclic prefix length

[0032] L short : Total length of short synchronization signal in MB-OFDM system

[0033] L 1,short : MB-OFDM system short synchronization signal layer 1 subsequence length

[0034] L 2,short : MB-OFDM system short synchronization signal layer 1 subsequence length

[0035] s short :Basic sequence of short synchronization signal in MB-OFDM system

[0036] s short,k : sequence s short The kth element of

[0037] Z short :The frequency domain subcarrier set Z in the process of generating short synchronization signal in MB-OFDM system short,n: Sequence Z short The nth element of

[0038] z short :Layer 1 time domain sequence of short synchronization signal in MB-OFDM system

[0039] y short :Layer 2 time domain sequence of short synchronization signal in MB-OFDM system

[0040] y short,j :y short The jth element of

[0041] g:Z short The first valid synchronization subcarrier number closest to the sideband in the negative half frequency

[0042] r:Z short The number of intervening subcarriers between adjacent valid synchronization subcarriers

[0043] V:Z short The number of effective synchronization subcarriers in

[0044] L long : The main sequence length of the long synchronization signal in the MB-OFDM system

[0045] L cp,long :The cyclic prefix length of the long synchronization signal in the MB-OFDM system

[0046] s long :Frequency domain basis sequence of long synchronization signal in MB-OFDM system

[0047] s long,k :s long The kth element of

[0048] Z long :Frequency domain subcarrier set in the long synchronization signal generation process of MB-OFDM system

[0049] z long :Z long The time domain sequence obtained after IDFT processing

[0050] Composition sequence s long Phase rotation number

[0051] u: baseband received signal of MB-OFDM system

[0052] R(τ): MB-OFDM system short synchronization signal autocorrelator output

[0053] P(d): Output of the second-layer unweighted combination of the short synchronization signal autocorrelation of the MB-OFDM system

[0054] E(d): Average power of received signal in MB-OFDM system

[0055] The maximum position of P(d) modulus

[0056] flag short :MB-OFDM system short synchronization signal synchronization success indication signal

[0057] Coarse frequency offset estimation results of short synchronization signal in MB-OFDM system

[0058] f s : Sampling rate of MB-OFDM system

[0059] R long (d) MB-OFDM system long synchronization signal autocorrelator output

[0060] Frequency offset estimation results of long synchronization signal subdivision multiples in MB-OFDM system

[0061] R long (d) Maximum position of the modulus

[0062] The method for generating a synchronization signal proposed by the present invention includes:

[0063] The main body of the synchronization signal is generated by performing outer product processing layer by layer on multiple layers of subsequences in the time domain.

[0064] The synchronization signal is at least used by the receiving end to detect and determine whether the signal transmitted in the channel is the signal expected to be received.

[0065] The synchronization signal may be located at the beginning of a physical frame or a physical block.

[0066] The synchronization signal can be used for carrier frequency offset estimation and timing synchronization.

[0067] The main body of the synchronization signal has a discrete time expression of

[0068]

[0069] Where s = {s i ,0≤i<L} is the discrete time sequence corresponding to the synchronization signal, and its length is L; x m ={x m,l ,0≤l<L m}, 1≤m≤M is the subsequence of the mth layer, with a length of L m ; M is the number of layers; The symbol represents the vector outer product (also called Kronecker product).

[0070] The processing method of the synchronization signal layer m (m>1) is:

[0071]

[0072] Among them, y m is the output result of the outer product of the mth layer (m>1), and its length is y0=x1. From this processing method, we can know that

[0073] In the method for generating the synchronization signal, the product of the lengths of the subsequences of each layer needs to be equal to the length of the synchronization signal, that is,

[0074] In the method for generating the synchronization signal, each layer output satisfies the weighted repetition characteristic. m Can be divided equally into L m The elements in the same position of any two subsequences differ only by the corresponding x m The weight of the sequence elements.

[0075] In the method for generating the synchronization signal, the sequence type and debugging method adopted by each layer of subsequence are independent of each other.

[0076] The synchronization signal can be directly generated in the time domain through the outer product, and then after up-sampling and shaping filtering, the desired transmission symbol rate and spectrum shape are obtained, and then sent to the digital-to-analog converter for transmission.

[0077] The synchronization signal can be directly generated in the time domain through the outer product, and the symbol rate is equal to the symbol rate of the final transmission; then the discrete Fourier transform (DFT) of point L is used to the frequency domain, and the spectrum is corrected in the frequency domain, and the values ​​at the subcarrier positions that do not require transmission power are set to 0; finally, the discrete inverse Fourier transform (IDFT) is performed back to the time domain and sent to the digital-to-analog converter for transmission.

[0078] The m-th layer output sequence y of the synchronization signal m , you can first pass L (m) The discrete Fourier transform (DFT) of the point is transformed into the frequency domain, and the spectrum is corrected in the frequency domain, and the values ​​at the subcarrier positions that do not need to transmit power are set to 0; finally, the inverse discrete Fourier transform (IDFT) is used to obtain the new time domain signal value, and the original y is refreshed. m The element value is then output to the next layer for use.

[0079] The synchronization signal can be repeated multiple times in the time domain to increase the diversity gain;

[0080] The method for generating a synchronization signal further generates a short synchronization signal with a length of L short In the time domain, it is manifested as a double-layer weighted repetitive structure, that is, the complete short synchronization signal consists of a length of L 1,short Layer 1 short time domain synchronization sequence {z short,i :i=0,1,...,L 1,short -1} and another 2,short The second-level random sequence {y short,j :j=0,1,...,L 2,short -1} is obtained by performing the outer product, where L short =L 1,short ·L 2,short The steps for generating a short synchronization signal are as follows:

[0081] The first step is to select a basic random sequence with relatively ideal PAPR and correlation characteristics, denoted as {s short,k :k=0,1,...,V}. Where V is the length of N DFT The number of synchronization subcarriers that can be placed in the frequency domain symbol.

[0082] The second step is to convert the sequence s short Map to a length of N according to a certain interval r DFT The frequency domain subcarrier set {Z shortn :n=-N DFT / 2,...,N DFT / 2-1}, the mapping method is as follows:

[0083]

[0084] Among them, Z short,p =s short,k , (-N DFT / 2≤p<N DFT / 2) is the synchronization sequence element at the effective subcarrier position in the frequency domain. In order to avoid DC interference in the transmitted signal, Z short The DC position is fixed to 0, that is, Z short,0 ≡0. The value of the synchronization sequence subcarrier number p is as follows:

[0085] p=g+k*r,0≤k≤V

[0086] Where g is Z short The first effective subcarrier number closest to the sideband in the negative half frequency; r is the number of interval subcarriers between adjacent effective subcarriers.

[0087] The third step is to short Perform IDFT processing to obtain a length of N DFTThe time domain synchronization symbol contains r identical lengths of L 1,short The first layer of short time domain sequence z short , and L 1,short r = N DFT .

[0088] Finally, the sequence z short With the length of the second layer being L 2,short The random sequence y short One way to do this is to convert the sequence z short In the time domain, first repeat L 2,short jth copy of sequence z short Overall and y short The jth element y short,j Multiply them together to get the jth part of the final short synchronization signal.

[0089] The present invention also proposes a method for generating a synchronization signal of a single-layer structure, characterized in that the time domain structure includes two parts: a cyclic prefix and a synchronization signal main sequence. The main sequence of the long synchronization signal (length L long =2N DFT ) in the time domain is a double repetitive structure, that is, a length of N DFT The synchronization sequence {z long,i :i=0,1,...,L 1,long -1} is generated by repeating twice in the time domain. The cyclic prefix is ​​a long synchronization signal main sequence tail length L in the time domain cp,long (0<L cp,long <N DFT ) part. The total length of the long sync signal is L long +L cp,long The steps for generating the long synchronization signal are as follows:

[0090] The first step is to select a basic random sequence with relatively ideal PAPR and correlation characteristics, denoted as {s long,k :k=0,1,...,V}. Where V is the length of N DFT The number of synchronization subcarriers that can be placed in the frequency domain symbol.

[0091] The second step is to synchronize the sequence s long Map to a length N according to the following rules DFT The frequency domain subcarrier set {Z long,n :n=-N DFT / 2,...,N DFT / 2-1}:

[0092]

[0093] The third step is tolong Perform inverse discrete Fourier transform IDFT processing to obtain a length of N DFT The sequence z long .

[0094] The fourth step is to convert the sequence z long Repeat twice in the time domain as the main part of the long synchronization signal;

[0095] Finally, the tail length of the long synchronization signal body part is L cp,long A partial copy of the signal is multiplexed to the front end as a cyclic prefix, and finally a complete long synchronization signal is obtained.

[0096] The present invention also proposes a method for generating a synchronization signal of a physical layer communication system, which includes two synchronization signals, a short synchronization signal in the front and a long synchronization signal in the back. The main body of the short synchronization signal is generated by performing outer product processing of multiple layers of subsequences layer by layer in the time domain.

[0097] In the method for generating a synchronization signal of a physical layer communication system, the long synchronization signal belongs to a single-layer structure, and its main body is presented as a double-repeated structure in the time domain.

[0098] The present invention also proposes a method for receiving a synchronization signal, comprising the following steps:

[0099] The processing step is to perform spectrum shifting, matched filtering and down-sampling on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion to obtain a processed baseband signal;

[0100] The detection step uses the weighted repetitive characteristics of each layer of the synchronization signal to perform delayed autocorrelation processing layer by layer. When performing delayed autocorrelation on each layer, the weighted coefficient of the layer needs to be removed in order to restore the unmodulated autocorrelation result. After the autocorrelation result is normalized and compared with the preset threshold, it can be determined whether the expected received signal may exist in the received signal. The position of the normalized correlation peak that exceeds the threshold indicates the timing synchronization information, and the peak phase indicates the frequency synchronization information, thereby completing frame boundary synchronization, symbol timing synchronization, and carrier frequency synchronization.

[0101] The main body of the synchronization signal is generated in the time domain by performing outer product processing on multiple layers of subsequences layer by layer.

[0102] The present invention also proposes a synchronization signal receiving device, comprising:

[0103] A processing unit performs spectrum shifting, matched filtering and down-sampling on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion to obtain a processed baseband signal;

[0104] The detection unit uses the weighted repetition characteristics of each layer of the synchronization signal to perform delayed autocorrelation processing layer by layer. When performing delayed autocorrelation on each layer, the weighted coefficient of the layer needs to be removed in order to restore the unmodulated autocorrelation result. After the autocorrelation result is normalized and compared with the preset threshold, it can be determined whether the expected received signal may exist in the received signal. The position of the normalized correlation peak that exceeds the threshold indicates the timing synchronization information, and the peak phase indicates the frequency synchronization information, thereby completing frame boundary synchronization, symbol timing synchronization, and carrier frequency synchronization.

[0105] The main body of the synchronization signal is generated in the time domain by performing outer product processing on multiple layers of subsequences layer by layer.

[0106] Furthermore, for the above-mentioned physical layer communication system including a short synchronization signal and a long synchronization signal, the present invention proposes a method for receiving a synchronization signal of the physical layer communication system, comprising the following steps:

[0107] Step 1: Perform digital front-end processing on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion, including spectrum shifting, matched filtering and downsampling, to obtain the processed baseband signal.

[0108] Step 2: According to the length L of the first layer sequence of the short synchronization signal 1,short The first layer delay autocorrelation of the received baseband signal is calculated by the delay amount and the correlation accumulation window length, and the delay autocorrelation R(τ) of the received signal u is defined as follows:

[0109]

[0110] Step 3: R(τ) according to L 1,short is the delay amount, according to L 2,short -1 is the number of accumulations, and the delayed accumulation of the second layer is performed to obtain the final autocorrelation result P(d):

[0111]

[0112] Step 4: Calculate the average power E(d) of the received signal. The calculation method is as follows:

[0113]

[0114] Note that this step can be processed in parallel with the previous steps in the hardware circuit;

[0115] Step 4: Search for the peak of the autocorrelation P(d) within the preset synchronous search window. The peak position is recorded as

[0116]

[0117] Where argmax(x) means searching for the maximum value of x.

[0118] Step 5: After the preset autocorrelation threshold is weighted by the average power of the received signal, it is compared with the searched peak value to obtain the autocorrelation synchronization success indication flag. short (1 means the synchronization is successful, 0 means it is unsuccessful)

[0119]

[0120] Step 6, if flag short If flag is equal to 0, it means that no valid MB-OFDM signal has been found and it is necessary to return to step 1 to continue searching. short If it is equal to 1, it means that a valid MB-OFDM signal has been captured, the frequency offset is estimated using the correlation peak, and the estimated frequency offset and peak position are output as the synchronization result, and the system state machine enters the long synchronization signal synchronization phase starting from step 7. The frequency offset calculation method is as follows

[0121]

[0122] Here, arg(x) indicates the angle at which to calculate x.

[0123] Step 7: Insert the frequency deviation compensation module to compensate for the frequency deviation. The symbol timing is adjusted, and the boundary position of the long synchronization signal is calculated according to the length of the short synchronization signal sequence, and the long synchronization signal is cut out from the received signal.

[0124] Step 8: Receive the long synchronization signal according to L 1,long is the delay, L 1,long For the accumulation window, calculate the delay-related value:

[0125]

[0126] Detailed estimation results of residual frequency offset Calculated from the phase of the autocorrelation peak:

[0127]

[0128]

[0129] in, represents the autocorrelation peak position.

[0130] Step 9: A frequency offset compensation module is placed to further compensate for the frequency offset. A cross-correlation operation is performed on the long synchronization signal, and accurate symbol timing is obtained based on the cross-correlation peak position.

[0131] Compared with the prior art, the technical solution proposed by the present invention has the following beneficial effects:

[0132] The synchronization signal has a weighted repetitive characteristic in the time domain, and can be synchronized using low-complexity delayed autocorrelation. By carefully designing the sequence of each layer, the peak-to-peak flattening phenomenon unique to traditional delayed autocorrelation processing can be eliminated, while almost no loss in signal-to-noise ratio or processing gain.

[0133] The synchronization signal can obtain various lengths and time domain repetition granularity characteristics by flexibly configuring the number of layers, the length of each layer subsequence and the number of diversity times, and can flexibly meet the different requirements of different communication systems for fast synchronization, correlation gain and other performances.

[0134] The synchronization signal no longer relies on or emphasizes the time domain constant mode characteristic in reducing PAPR. Good low PAPR characteristics can be achieved through the PAPR optimization design and combination of sub-sequences of each layer.

[0135] The synchronization signal supports two modes of generation: time domain generation and frequency domain generation. The generation mode can be flexibly selected for single-carrier systems or multi-carrier systems to match the hardware complexity requirements of the transmitter. For a single-carrier system, the synchronization signal can be directly generated in the time domain, and then multiplexed with other payload data, and sent to the digital-to-analog converter after a unified up-sampling and shaping filter matching rate and spectrum template. For multi-carrier systems such as OFDM, a frequency domain synchronization sequence matching the spectrum template can be generated in advance, and then the time domain signal can be generated using the existing inverse fast Fourier transform (IFFT) module, and the outer product processing of the next few layers is completed in the time domain, and the cyclic prefix is ​​multiplexed and sent to the analog-to-digital converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0136] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute a limitation of the present invention. In the drawings:

[0137] Figure 1 It is a schematic diagram of the hierarchical synchronization signal composition of the present invention;

[0138] Figure 2 It is a schematic diagram of a time domain generation method of a hierarchical synchronization signal of the present invention;

[0139] Figure 3 It is a schematic diagram of a transmission spectrum shaping method of a hierarchical synchronization signal of the present invention;

[0140] Figure 4It is a schematic diagram of a layer-by-layer spectrum shaping method of a layered synchronization signal of the present invention;

[0141] Figure 5 It is a schematic diagram of a time-repeated diversity transmission method of a hierarchical synchronization signal according to the present invention;

[0142] Figure 6 It is a schematic diagram of a method for multiplexing a cyclic prefix of a layered synchronization signal in the time domain of the present invention;

[0143] Figure 7 It is a schematic diagram of the physical frame structure of the MB-OFDM system of the present invention;

[0144] FIG8(a) is a schematic diagram of the short synchronization signal structure of the MB-OFDM system transmission modes 0 and 1 of the present invention

[0145] FIG8( b ) is a schematic diagram of the short synchronization signal structure of the MB-OFDM system transmission mode 2 of the present invention

[0146] FIG8(c) is a schematic diagram of the short synchronization signal structure of the MB-OFDM system transmission modes 3 and 4 of the present invention.

[0147] Fig. 9 This is a schematic diagram of the long synchronization signal structure of the MB-OFDM system of the present invention.

[0148] Fig.10 This is a schematic diagram of the MB-OFDM system synchronization signal reception and processing of the present invention. DETAILED DESCRIPTION

[0149] In order to make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings. Here, the schematic implementation of the present invention and its description are used to explain the present invention, but are not intended to limit the present invention. The terms "unit" or "module" used below can be hardware, software or a combination of the two to achieve a predetermined function. When the embodiment is described in one of the implementation modes, the other two modes can also achieve the intention of the present invention, and therefore also belong to the contribution scope of the present invention.

[0150] First, the English symbols involved in this embodiment are explained as follows:

[0151] DFT: Discrete Fourier Transform

[0152] IDFT: Inverse Discrete Fourier Transform

[0153] OFDM: Orthogonal Frequency Division Multiplexing

[0154] MB-OFDM: Multi-Bandwidth Orthogonal Frequency Division Multiplexing

[0155] BPSK: Binary Frequency Shift Keying

[0156] PAPR: Peak power to average power ratio

[0157] CM: Cubic Metrics

[0158] s: hierarchical synchronization signal according to the present invention

[0159] x m : The mth layer subsequence of the layered synchronization signal of the present invention

[0160] L: length of the hierarchical synchronization signal according to the present invention

[0161] M: the number of layers of the hierarchical synchronization signal described in the present invention

[0162] L m :sequence x m Length

[0163] y m : The mth layer output result of the hierarchical synchronization signal of the present invention

[0164] L (m) :y m Length

[0165] N DFT :DFT points

[0166] L cp : Cyclic prefix length

[0167] N_fc: Number of frame control symbols in MB-OFDM system

[0168] N_pld: Number of payload data symbols in the MB-OFDM system

[0169] L short : Total length of short synchronization signal in MB-OFDM system

[0170] L 1,short : MB-OFDM system short synchronization signal layer 1 subsequence length

[0171] L 2,short : MB-OFDM system short synchronization signal layer 1 subsequence length

[0172] s short :Basic sequence of short synchronization signal in MB-OFDM system

[0173] s short,k : sequence s short The kth element of

[0174] Z short:Frequency domain subcarrier set in the process of short synchronization signal generation in MB-OFDM system

[0175] Z short,n : Sequence Z short The nth element of

[0176] z short :Layer 1 time domain sequence of short synchronization signal in MB-OFDM system

[0177] y short :Layer 2 time domain sequence of short synchronization signal in MB-OFDM system

[0178] y short,j :y short The jth element of

[0179] g:Z short The first valid synchronization subcarrier number closest to the sideband in the negative half frequency

[0180] r:Z short The number of intervening subcarriers between adjacent valid synchronization subcarriers

[0181] V:Z short The number of effective synchronization subcarriers in

[0182] L long : The main sequence length of the long synchronization signal in the MB-OFDM system

[0183] L cp,long :The cyclic prefix length of the long synchronization signal in the MB-OFDM system

[0184] s long :Frequency domain basis sequence of long synchronization signal in MB-OFDM system

[0185] s long,k :s long The kth element of

[0186] Z long :Frequency domain subcarrier set in the long synchronization signal generation process of MB-OFDM system

[0187] z long :Z long The time domain sequence obtained after IDFT processing

[0188] Composition sequence s long Phase rotation number

[0189] u: baseband received signal of MB-OFDM system

[0190] R(τ): MB-OFDM system short synchronization signal autocorrelator output

[0191] P(d): Output of the second-layer unweighted combination of the short synchronization signal autocorrelation of the MB-OFDM system

[0192] E(d): Average power of received signal in MB-OFDM system

[0193] The maximum position of P(d) modulus

[0194] flag short :MB-OFDM system short synchronization signal synchronization success indication signal

[0195] Coarse frequency offset estimation results of short synchronization signal in MB-OFDM system

[0196] f s : Sampling rate of MB-OFDM system

[0197] R long (d) MB-OFDM system long synchronization signal autocorrelator output

[0198] Frequency offset estimation results of long synchronization signal subdivision multiples in MB-OFDM system

[0199] R long (d) Maximum position of the modulus

[0200] Synchronization signals are widely used in physical layer communication systems. They are used by the receiving end to detect whether the signal transmitted in the channel is the desired signal, and are further used for carrier frequency offset estimation and timing synchronization. In most cases, the synchronization signal is located at the beginning of a physical frame or physical block.

[0201] Figure 1 Schematic diagram of the hierarchical synchronization signal structure of the present invention. Figure 1 As shown, the main body of the hierarchical synchronization signal is generated by performing outer product processing on multiple layers of subsequences layer by layer in the time domain, and its discrete time expression is:

[0202]

[0203] Where s = {s i ,0≤i<L} is the discrete time sequence corresponding to the hierarchical synchronization signal, and its length is L; x m ={x m,l ,0≤l<L m}, 1≤m≤M is the subsequence of the mth layer, with a length of L m ; M is the number of layers; The symbol represents the vector outer product (also called Kronecker product). The method for processing the outer product at the mth (1<m≤M) level is:

[0204]

[0205] Among them, y m is the output result of the outer product of the mth layer (m>1), and its length is When m=1, y1=x1. The product of the lengths of the subsequences of each layer needs to be equal to the length of the synchronization signal, that is,

[0206] Each layer output of the hierarchical synchronization signal satisfies the time domain weighted repetition characteristic. m Can be divided equally into L m The elements in the same position of any two subsequences differ only by the corresponding x m The weights of the sequence elements. This weighted repetition in the time domain allows synchronization processing with low-complexity delayed autocorrelation at the receiver. By carefully designing the sequences of each layer, the peak-to-peak flattening phenomenon characteristic of traditional delayed autocorrelation processing can be eliminated with almost no loss in signal-to-noise ratio or processing gain.

[0207] The length of each layer subsequence of the layered synchronization signal, the sequence type and debugging method used are configured independently. The layered synchronization signal can obtain various lengths and time domain repetition granularity characteristics by flexibly configuring the number of layers, the length of each layer subsequence and the number of diversity times. It can flexibly meet the different requirements of different communication systems for fast synchronization, correlation gain and other performance.

[0208] like Figure 2 As shown, the hierarchical synchronization signal can be directly generated in the time domain through the outer product, multiplexed with the physical layer payload data symbol, and then subjected to up-sampling, shaping filtering and rate matching to obtain the desired transmission symbol rate and spectrum shape, and then sent to the digital-to-analog converter and RF front end for transmission.

[0209] like Figure 3 As shown, the hierarchical synchronization signal can be directly generated in the time domain through the outer product, and the symbol rate is equal to the final transmitted symbol rate; then it is transformed to the frequency domain through the DFT of point L, and the spectrum is corrected in the frequency domain, and the values ​​at the subcarrier positions that do not require transmission power are set to 0; finally, the IDFT is transformed back to the time domain, and after being multiplexed with the physical layer payload data symbols after shaping filtering, it is sent to the digital-to-analog converter and the RF front end for transmission.

[0210] like Figure 4 As shown, the m-1th (m>2) layer output sequence y of the hierarchical synchronization signal m-1 , you can first pass L (m)The DFT of the point is transformed into the frequency domain, and the spectrum is corrected in the frequency domain, and the values ​​at the subcarrier positions that do not need to transmit power are set to 0; finally, the IDFT transformation is used to obtain the new time domain signal value, and the original y is refreshed. m-1 After the element value is calculated, the outer product of the mth layer is performed together with the mth layer subsequence.

[0211] like Figure 5 As shown, the hierarchical synchronization signal can be repeated N times (N≥1) in the time domain to increase the diversity gain;

[0212] like Figure 6 As shown, the layered synchronization signal with a length of L·N after N-fold time domain repetition can be replaced by a tail with a length of L in the time domain. cp The sequence copy is concatenated with the original sequence. This structure can make cp Any signal of length L·N in the +L·N length interval has the same signal characteristics as the cyclic shift of the original layer synchronization signal. This characteristic can be used to combat inter-symbol interference caused by multipath in OFDM multi-carrier systems.

[0213] The present invention proposes a method for receiving the hierarchical synchronization signal, the method comprising:

[0214] The processing step is to perform spectrum shifting, matched filtering and down-sampling on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion to obtain a processed baseband signal;

[0215] The detection step uses the weighted repetitive characteristics of each layer of the synchronization signal to perform delayed autocorrelation processing layer by layer. When performing delayed autocorrelation on each layer, the weighted coefficient of the layer needs to be removed in order to restore the unmodulated autocorrelation result. After the autocorrelation result is normalized and compared with the preset threshold, it can be determined whether the expected received signal may exist in the received signal. The position of the normalized correlation peak that exceeds the threshold indicates the timing synchronization information, and the peak phase indicates the frequency synchronization information, thereby completing frame boundary synchronization, symbol timing synchronization, and carrier frequency synchronization.

[0216] 11. A synchronization signal receiving device, characterized in that the device comprises:

[0217] A processing unit performs spectrum shifting, matched filtering and down-sampling on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion to obtain a processed baseband signal;

[0218] The detection unit uses the weighted repetition characteristics of each layer of the synchronization signal to perform delayed autocorrelation processing layer by layer. When performing delayed autocorrelation on each layer, the weighted coefficient of the layer needs to be removed in order to restore the unmodulated autocorrelation result. After the autocorrelation result is normalized and compared with the preset threshold, it can be determined whether the expected received signal may exist in the received signal. The position of the normalized correlation peak that exceeds the threshold indicates the timing synchronization information, and the peak phase indicates the frequency synchronization information, thereby completing frame boundary synchronization, symbol timing synchronization, and carrier frequency synchronization.

[0219] The present invention will provide a specific embodiment, which describes in detail how the synchronization signal constructed by the hierarchical synchronization signal construction method proposed in the present invention is applied to the MB-OFDM (multi-band orthogonal frequency division multiplexing) Internet of Things system to achieve the purpose of the present invention. The specific contents include:

[0220] MB-OFDM system communicates in burst mode, similar to IEEE 802.11a, using carrier sensing for competitive access. The requirement for synchronization is to identify whether there is a valid signal being transmitted in the channel in the shortest possible time; if there is a signal being transmitted, it is necessary to stably and reliably complete timing synchronization and frequency synchronization within the specified time. In order to adapt to different IoT rate throughput requirements, MB-OFDM system has designed 5 transmission modes with different bandwidths, supporting 3.2MHz, 1.6MHz, 0.8MHz, 0.4MHz and 0.2MHz bandwidths respectively. The specific system parameters are shown in the following table.

[0221] Table 1 System parameters of different transmission modes of MB-OFDM system

[0222]

[0223]

[0224] In each transmission mode, the number of frequency domain subcarriers and time domain baseband samples available for short synchronization signals and long synchronization signals is different, and the requirements for PAPR, timing synchronization and frequency synchronization are also different. In view of different system requirements under different transmission modes, the layered synchronization signal construction method proposed in the present invention is used to flexibly adopt different layered design parameters to construct a double-layer structure synchronization signal, called a short synchronization signal; and a synchronization signal with twice the repetition and cyclic prefix in a single-layer time domain is designed, called a long synchronization signal. The two synchronization signals are cascaded together to jointly complete faster and more accurate synchronization detection to adapt to burst communications. The short synchronization signal is used for energy detection, AGC control, fast timing capture and coarse frequency deviation estimation; the long synchronization signal is used for fine timing synchronization, fine frequency deviation estimation, channel estimation and reference phase estimation.

[0225] The physical layer frame structure of the MB-OFDM system is as follows: Figure 7 As shown in Figure 1. The physical layer frame consists of a short synchronization signal, a long synchronization signal, frame control, and payload data. The short synchronization signal is generated by the outer product of the two-layer subsequences, and the length of the first layer sequence is L. 1,short Shorter, layer 2 sequence length L 2,short Longer, without cyclic prefix, expressed as L in the time domain 2,short The segment length is L 1,short The long synchronization signal is a single-layer structure, which is represented by two segments of length L in the time domain. long The subsequence is repeated before and after and the length is L cp,long The characteristics of the cyclic prefix; the structure of the frame control symbol (the number is N_fc) and the payload data symbol (the number is N_pld) are consistent, and the classic OFDM structure is adopted, which is composed of a DFT data block plus a cyclic prefix. In order to suppress the out-of-band sidelobe leakage of the spectrum, a window function can be used to smooth the junction of adjacent OFDM time domain symbols. The roll-off area brought by the window function filtering is also included in the cyclic prefix length. However, the benefits brought by the time domain window function can also be obtained through other implementation methods, such as frequency domain filtering. The frame structure proposed in the present invention can support a window function or a non-window function (roll-off length is 0). The OFDM symbol structure involved in the following text, unless otherwise specified, refers to the non-window function.

[0226] The length of the short synchronization signal in different transmission modes of the MB-OFDM system is fixed to 5 DFT blocks (that is, the total sample length is L short =5N DFT ). In the time domain, it is manifested as a double-layer weighted repetitive structure, that is, the complete short synchronization signal consists of a length of L 1,short Layer 1 short time domain synchronization sequence {z short,i :i=0,1,...,L 1,short -1} and another2,short The second-level random sequence {y short,j :j=0,1,...,L 2,short -1} is obtained by performing the outer product, where L short =L 1,short ·L 2,short =5·N DFT .

[0227] The present invention provides a method for generating a short synchronization signal as follows:

[0228] The first step is to select a basic random sequence with relatively ideal PAPR and correlation characteristics, denoted as {s short,k :k=0,1,...,V}. Where V is the length of N in the transmission mode option specified in the MB-OFDM system. DFT The number of synchronization subcarriers that can be placed in the frequency domain symbol.

[0229] The second step is to convert the sequence s short Map to a length of N according to a certain interval r DFT The frequency domain subcarrier set {Z short,n :n=-N DFT / 2,...,N DFT / 2-1}, the mapping method is as follows:

[0230]

[0231] Among them, Z short,p =s short,k , (-N DFT / 2≤p<N DFT / 2) is the synchronization sequence element at the effective subcarrier position in the frequency domain. In order to avoid DC interference in the transmitted signal, the DC position of the frequency domain OFDM symbol is fixed to 0, that is, Z short,0 ≡0. The value of the synchronization sequence subcarrier number p is as follows:

[0232] p=g+k*r,0≤k≤V

[0233] Among them, g is the first effective subcarrier number closest to the sideband in the negative half frequency of OFDM frequency domain data; r is the number of interval subcarriers between adjacent effective subcarriers.

[0234] The third step is to short Perform IDFT processing to obtain a length of N DFT The time domain synchronization symbol contains r identical lengths of L 1,short The first layer of short time domain sequence z short , and L 1,short r = N DFT .

[0235] Finally, the sequence z short With the length of the second layer being L 2,short The random sequence y short One way to do this is to convert the sequence z short In the time domain, first repeat L 2,short jth copy sequence z short Overall and y short The jth element y short,j Multiply them together to get the jth part of the final short synchronization signal.

[0236] In different bandwidth transmission modes, the present invention provides key parameter values ​​in the above steps as shown in the following table.

[0237] Table 2 Key parameter values ​​of short synchronization signals under different transmission mode options

[0238]

[0239]

[0240] A schematic diagram of the time domain structure of the short synchronization signal in different transmission modes of the MB-OFDM system is shown in Figure 8. Figure 8(a) shows the short synchronization signal structure of transmission modes 0 and 1, Figure 8(b) shows the short synchronization signal structure of transmission mode 2, and Figure 8(c) shows the short synchronization signal structure of transmission modes 3 and 4.

[0241] The frequency domain basic sequence s provided by the present invention short is a truncated and BPSK modulated binary random sequence. The first layer sequence z generated by this sequence short It has good cyclic autocorrelation and cross-correlation characteristics, and very low PAPR. short The excellent characteristics determine that the correlation characteristics and PAPR indicators of the final short synchronization signal sequence are relatively ideal. The PAPR of the short synchronization signal sequence in the five transmission modes is 2.75dB, 1.76dB, 1.76dB, 1.76dB and 1.25dB respectively, which is much lower than the PAPR of the data OFDM symbol (usually higher than 8dB). This allows the transmission power of the short synchronization signal to be further increased, improving the received signal-to-noise ratio and synchronization robustness.

[0242] The second layer sequence y provided by the present invention short is a binary random sequence, whose value determines the polarity change of the sequence after the outer product. shortIf the elements of are all 1, the time domain structure of the short synchronization signal degenerates into a single-layer structure similar to that used in the IEEE802.11a system. The single-layer structure is relatively simple to implement for the transmitter, but if the delayed autocorrelation processing method is used at the receiving end, the autocorrelation result will have obvious peaks and flat layers. Even in a single-path channel environment, the timing synchronization result will have a large deviation. By increasing L 2,short The peak-to-peak flattening effect can be eliminated by adding a numerical value or superimposing and averaging the autocorrelation results again, but the related noise term will be significantly increased, which will deteriorate the signal-to-noise ratio or processing gain. The multi-layer structure of the present invention can eliminate the peak-to-peak flattening effect and improve the timing synchronization performance while maintaining almost no loss in the signal-to-noise ratio. short The value of is not unique, and any sequence that can achieve a similar purpose can be applied.

[0243] As mentioned above, if y short If the values ​​of the elements of are all 1, it degenerates into a single-layer structure. The present invention also provides a specific method for generating a synchronization sequence of a single-layer structure.

[0244] The length of the long synchronization signal is fixed at 2.5 DFT blocks, and is characterized by a single-layer synchronization sequence structure, including a length of half the DFT block length (L cp,long =N DFT / 2) and a synchronization signal body with a length of two DFT blocks. The main sequence of the long synchronization signal (length L long =2N DFT ) in the time domain is a double repetitive structure, that is, a length of N DFT The synchronization sequence {z long,i :i=0,1,...,L 1,long -1} is generated twice in the time domain. The time domain structure diagram of the long synchronization signal is as follows Fig. 9 Shown

[0245] The present invention provides a method for generating a long synchronization signal as follows:

[0246] The first step is to select a basic random sequence with relatively ideal PAPR and correlation characteristics, denoted as {s long,k :k=0,1,...,V}. Where V is the length of N in the transmission mode option specified in the MB-OFDM system. DFT The number of synchronization subcarriers that can be placed in the frequency domain symbol.

[0247] The second step is to synchronize the sequence s long Map to a length N according to the following rules DFT The frequency domain subcarrier set {Z long,n :n=-N DFT / 2,...,NDFT / 2-1}:

[0248]

[0249] The third step is to long Perform IDFT processing to obtain a length of N DFT The sequence z long .

[0250] The fourth step is to convert the sequence z long Repeat twice in the time domain as the main part of the long synchronization signal;

[0251] Finally, the tail length of the long synchronization signal body part is L cp,long =N DFT A partial copy of / 2 is multiplexed to the front end as a cyclic prefix, and finally a complete long synchronization signal is obtained.

[0252] The long synchronization signal frequency domain basic sequence s provided by the present invention long Different sequence designs are used in five different bandwidth transmission modes. For transmission modes 0, 1 and 2, the bandwidth is relatively large and the PAPR requirement is relatively high. The constant modulus multi-phase sequence is used as the basic sequence, which can reduce the PAPR while maintaining excellent correlation characteristics. For transmission modes 3 and 4, the bandwidth is small and the PAPR is better controlled. However, due to the small r used by the short synchronization signal, the frequency deviation range that can be estimated is limited, and it is necessary to design a synchronization sequence that is insensitive to frequency deviation and timing deviation. After comparison, in transmission modes 3 and 4, a BPSK modulated binary random sequence similar to the short synchronization signal is used. According to the sequence design provided by the present invention, the PAPR of the long synchronization signal in the five transmission modes is 2.75dB, 1.76dB, 1.76dB, 1.76dB and 1.25dB, respectively, which is much lower than the PAPR of the data OFDM symbol (usually higher than 8dB), which allows the transmission power of the long synchronization signal to be further increased, thereby improving the received signal-to-noise ratio and the robustness of synchronization.

[0253] The present invention provides a long synchronization signal frequency domain basic sequence s long The generation methods in five transmission modes are as follows:

[0254] For transmission mode 0, sequence s long The generation method is:

[0255]

[0256] in, is the phase rotation number of the sequence, and its values ​​are shown in the following table.

[0257] Table 3 Phase rotation number values ​​of the long synchronization signal basic sequence in transmission mode 0

[0258]

[0259]

[0260]

[0261] For transmission mode 1, sequence s long The generation method is:

[0262]

[0263] in, is the phase rotation number of the sequence, and its values ​​are shown in the following table.

[0264] Table 4 Phase rotation number values ​​of the long synchronization signal basic sequence in transmission mode 1

[0265]

[0266]

[0267] For transmission mode 2, sequence s long The generation method is:

[0268]

[0269] in, is the phase rotation number of the sequence, and its values ​​are shown in the following table.

[0270] Table 5 Phase rotation number values ​​of the long synchronization signal basic sequence in transmission mode 2

[0271]

[0272] For transmission mode 3, the sequence s long is a BPSK binary random sequence, directly mapped to Z long The results are shown in the following table:

[0273] Table 6 Values ​​of basic sequence elements of long synchronization signal in transmission mode 3

[0274]

[0275]

[0276] For transmission mode 4, the sequence s long is a BPSK binary random sequence, directly mapped to Z long The results are shown in the following table:

[0277] Table 6 Values ​​of basic sequence elements of long synchronization signal in transmission mode 4

[0278]

[0279] The process of the physical layer system synchronization signal receiving method proposed by the present invention is as follows: Fig.10 As shown:

[0280] Step 1: Perform digital front-end processing on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion, including spectrum shifting, matched filtering and downsampling, to obtain the processed baseband signal.

[0281] Step 2: According to the length L of the first layer sequence of the short synchronization signal 1,short The first layer delay autocorrelation of the received baseband signal is calculated by the delay amount and the correlation accumulation window length, and the delay autocorrelation R(τ) of the received signal u is defined as follows:

[0282]

[0283] Step 3: R(τ) according to L 1,short is the delay amount, according to L 2,short -1 is the number of accumulations, and the delayed accumulation of the second layer is performed to obtain the final autocorrelation result P(d):

[0284]

[0285] Step 4: Calculate the average power E(d) of the received signal. The calculation method is as follows:

[0286]

[0287] Note that this step can be processed in parallel with the previous steps in the hardware circuit;

[0288] Step 4: Search for the peak of the autocorrelation P(d) within the preset synchronous search window. The peak position is recorded as

[0289]

[0290] Where argmax(x) means searching for the maximum value of x.

[0291] Step 5: After the preset autocorrelation threshold is weighted by the average power of the received signal, it is compared with the searched peak value to obtain the autocorrelation synchronization success indication flag. short (1 means the synchronization is successful, 0 means it is unsuccessful)

[0292]

[0293] Step 6, if flag short If flag is equal to 0, it means that no valid MB-OFDM signal has been found and it is necessary to return to step 1 to continue searching. short If it is equal to 1, it means that a valid MB-OFDM signal has been captured, the frequency offset is estimated using the correlation peak, and the estimated frequency offset and peak position are output as the synchronization result, and the system state machine enters the long synchronization signal synchronization phase starting from step 7. The frequency offset calculation method is as follows

[0294]

[0295] Here, arg(x) indicates the angle at which to calculate x.

[0296] Step 7: Insert the frequency deviation compensation module to compensate for the frequency deviation. The symbol timing is adjusted, and the boundary position of the long synchronization signal is calculated according to the length of the short synchronization signal sequence, and the long synchronization signal is cut out from the received signal.

[0297] Step 8: Receive the long synchronization signal according to L 1,long is the delay, L 1,long For the accumulation window, calculate the delay-related value:

[0298]

[0299] Detailed estimation results of residual frequency offset Calculated from the phase of the autocorrelation peak:

[0300]

[0301]

[0302] in, represents the autocorrelation peak position.

[0303] Step 9: A frequency offset compensation module is placed to further compensate for the frequency offset. A cross-correlation operation is performed on the long synchronization signal, and accurate symbol timing is obtained based on the cross-correlation peak position.

[0304] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0305] It should be noted and understood that various modifications and improvements can be made to the invention described in detail above without departing from the spirit and scope of the invention as claimed in the preceding claims. Therefore, the scope of the claimed technical solution is not limited by any specific exemplary teaching given.

Claims

1. A method for generating a synchronization signal of a physical layer communication system, characterized in that: The physical layer communication system synchronization signal includes a short synchronization signal and a long synchronization signal, wherein the short synchronization signal is in front and the long synchronization signal is in the back, specifically: The main body of the short synchronization signal is generated by performing outer product processing layer by layer on multiple subsequences in the time domain. The discrete time expression of the main body of the short synchronization signal is: Where s = {s i ,0≤i<L} is the discrete time sequence corresponding to the short synchronization signal, and its length is L; x m ={x m,l ,0≤l<L m }, 1≤m≤M is the subsequence of the mth layer, with a length of L m ; M is the number of layers; The symbol represents the vector outer product; Generate a short synchronization signal, the length of which is L short ; It is manifested as a double-layer weighted repetitive structure in the time domain, that is, the complete short synchronization signal consists of a length of L 1,short The first layer short time domain synchronization sequence {z short,i :i=0,1,...,L 1,short -1} and another 2,short The second-level random sequence {y short,j :j=0,1,...,L 2,short -1} is obtained by performing the outer product, where L short =L 1,short ·L 2,short ; The steps of generating the short synchronization signal are as follows: The first step is to select a basic random sequence, denoted as {s short,k :k=0,1,...,V}; where V is the length of N in the transmission mode option specified in the MB-OFDM system DFT The number of synchronization subcarriers that can be placed in the frequency domain symbol; The second step is to convert the sequence s short Map to a length of N according to a certain interval r DFT The frequency domain subcarrier set {Z short,n :n=-N DFT / 2,...,N DFT / 2-1}, the mapping method is as follows: Among them, -N DFT / 2≤p<N DFT / 2,Z short,p =s short,k , is the synchronization sequence element at the effective subcarrier position in the frequency domain; Z short The DC position is fixed to 0, that is, Z short,0 ≡0; the value of the synchronization sequence subcarrier number p is as follows: p=g+k*r,0≤k≤V Where g is Z short The first valid subcarrier number closest to the sideband in the negative half frequency; r is the number of subcarriers between adjacent valid subcarriers, V is Z short The number of effective synchronization subcarriers in; The third step is to short Perform inverse discrete Fourier transform IDFT processing to obtain a length of N DFT The time domain synchronization symbol contains r identical lengths of L 1，short The first layer of short time domain sequence z short , and L 1，short r = N DFT ; Finally, the sequence z short With the length of the second layer being L 2，short The random sequence y short Perform the outer product, that is, the sequence z short In the time domain, first repeat L 2，short jth copy of sequence z short Overall and y short The jth element y short，j Multiply them together to obtain the jth part of the final short synchronization signal; MB-OFDM system is a communication system that uses OFDM as the physical layer transmission technology and can support multi-rate transmission; The MB-OFDM system supports five transmission modes with different transmission rates. The system parameters of each transmission mode are shown in the following table: Generate a long synchronization signal, whose time domain structure includes two parts: cyclic prefix and long synchronization signal main sequence; the length of the long synchronization signal main sequence is L long =2N DFT , which appears as a double repetitive structure in the time domain, that is, a length of N DFT The synchronization sequence {z long，i :i=0,1,...,L 1，long -1} is generated by repeating twice in the time domain; the cyclic prefix is ​​a long synchronization signal in the time domain, and the tail length of the main sequence is L cp，long Partial replication, 0<L cp，long <N DFT The total length of the long synchronization signal is L long +L cp，long ; The steps for generating the long synchronization signal are as follows: The first step is to select a basic random sequence, denoted as {s long,k :k=0,1,...,V}; where V is the length of N in the transmission mode option specified in the MB-OFDM system DFT The number of synchronization subcarriers that can be placed in the frequency domain symbol; The second step is to synchronize the sequence s long Map to a length N according to the following rules DFT The frequency domain subcarrier set {Z long,n :n=-N DFT / 2,...,N DFT / 2-1}: The third step is to long Perform IDFT processing to obtain a length of N DFT The sequence z long ; The fourth step is to convert the sequence z long Repeat twice in the time domain as the main part of the long synchronization signal; Finally, the tail of the long synchronization signal body is L cp,long The partial copy is multiplexed to the front end as a cyclic prefix, and finally a complete long synchronization signal is obtained; The English symbols are defined as follows: OFDM: Orthogonal Frequency Division Multiplexing MB-OFDM: Multi-Bandwidth Orthogonal Frequency Division Multiplexing CP: Cyclic Prefix N DFT : DFT score s short :Basic sequence of short synchronization signal in MB-OFDM system s short,k : sequence s short The kth element of Z short :Frequency domain subcarrier set in the process of short synchronization signal generation in MB-OFDM system Z short,n : Sequence Z short The nth element of z short :The first layer time domain sequence of short synchronization signal in MB-OFDM system y short :Layer 2 time domain sequence of short synchronization signal in MB-OFDM system y short,j :y short The jth element of L cp,long :The cyclic prefix length of the long synchronization signal in the MB-OFDM system L long : The main sequence length of the long synchronization signal in the MB-OFDM system s long :Frequency domain basis sequence of long synchronization signal in MB-OFDM system s long,k :s long The kth element of Z long : Frequency domain subcarrier set in the long synchronization signal generation process of MB-OFDM system z long :Z long The time domain sequence obtained after IDFT processing.

2. The method according to claim 1, characterized in that The short synchronization signal is at least used by the receiving end to detect and determine whether the signal transmitted in the channel is a signal that is expected to be received.

3. The method according to claim 1, characterized in that The short synchronization signal is located at the beginning of a physical frame or a physical block.

4. The method according to claim 1, characterized in that The short synchronization signal is used for carrier frequency offset estimation and timing synchronization.

5. The method according to claim 1, characterized in that The method for processing the m-th layer outer product of the short synchronization signal is: Among them, y m is the output result of the outer product of the mth layer, and its length is y0=x1.

6. The method according to claim 1, characterized in that The product of the lengths of the subsequences of each layer of the short synchronization signal needs to be equal to the length of the short synchronization signal, that is, 7. The method according to claim 1, characterized in that Each layer output of the short synchronization signal satisfies the weighted repetition characteristic, that is, y m Can be divided equally into L m The elements in the same position of any two subsequences differ only by the corresponding x m The weight of the sequence elements.

8. The method according to claim 1, characterized in that: The sequence type and debugging method used by each layer subsequence of the short synchronization signal are independent of each other.

9. The method according to claim 1, characterized in that The short synchronization signal can be directly generated in the time domain through outer product, and then after up-sampling and shaping filtering, the desired transmission symbol rate and spectrum shape are obtained, and then sent to the digital-to-analog converter for transmission.

10. The method according to claim 1, characterized in that The short synchronization signal can be directly generated in the time domain through the outer product, and the symbol rate is equal to the symbol rate of the final transmission; then the L-point discrete Fourier transform DFT is used to the frequency domain, and the spectrum is corrected in the frequency domain, and the value at the subcarrier position that does not require transmission power is set to 0; Finally, the L-point IDFT is performed back to the time domain and sent to the digital-to-analog converter for transmission.

11. The method according to claim 5, characterized in that The short synchronization signal layer m output sequence y m , you can first pass L (m) The DFT of the point is transformed into the frequency domain, and the spectrum is corrected in the frequency domain, and the values ​​at the subcarrier positions that do not require transmission power are set to 0; finally, L (m) Point IDFT to get the new time domain signal value and refresh the original y m The element value is then output to the next layer for use.

12. The method according to claim 1, characterized in that The short synchronization signal is repeated multiple times in the time domain to increase the diversity gain.

13. The method according to claim 1, characterized in that The short synchronization signal has different key parameter values ​​in different bandwidth transmission modes. The key parameter values ​​in typical transmission modes are shown in the following table: The English symbols are defined as follows: N DFT : DFT score g:Z short The first valid synchronization subcarrier number closest to the sideband in the negative half frequency r:Z short The number of intervening subcarriers between adjacent valid synchronization subcarriers V:Z short The number of effective synchronization subcarriers in L 1,short : MB-OFDM system short synchronization signal layer 1 subsequence length L 2,short : MB-OFDM system short synchronization signal layer 1 subsequence length s short :Basic sequence of short synchronization signal in MB-OFDM system y short :The second layer time domain sequence of the short synchronization signal in the MB-OFDM system.

14. The method according to claim 1, wherein: The long synchronization signal frequency domain basic sequence s long The generation methods in the five transmission modes of the MB-OFDM system are as follows: For transmission mode 0, sequence s long The generation method is: in, is the phase rotation number of the sequence, and its values ​​are shown in the following table: For transmission mode 1, sequence s long The generation method is: in, is the phase rotation number of the sequence, and its values ​​are shown in the following table: For transmission mode 2, sequence s long The generation method is: in, is the phase rotation number of the sequence, and its values ​​are shown in the following table: For transmission mode 3, the sequence s long is a binary random sequence modulated by BPSK, which is directly mapped to Z long The results are shown in the following table: For transmission mode 4, the sequence s long is a binary random sequence modulated by BPSK, which is directly mapped to Z long The results are shown in the following table: The English symbols are defined as follows: OFDM: Orthogonal Frequency Division Multiplexing MB-OFDM: Multi-Bandwidth Orthogonal Frequency Division Multiplexing BPSK: Binary Phase Shift Keying s long :Frequency domain basis sequence of long synchronization signal in MB-OFDM system s long,k :s long The kth element of Z long : Frequency domain subcarrier set in the long synchronization signal generation process of MB-OFDM system Composition sequence s long Phase rotation number n: frequency domain subcarrier number of the MB-OFDM system.

15. A method for receiving a physical layer communication system synchronization signal generated by any one of the methods of claims 1 to 14, characterized in that: The following steps are included: Step 1, performing digital front-end processing on the high-multiple sampled intermediate frequency or zero intermediate frequency digital signal received after analog-to-digital conversion, including spectrum shifting, matched filtering and downsampling processing, to obtain a processed baseband signal; Step 2: According to the length L of the first layer sequence of the short synchronization signal 1,short The first layer delay autocorrelation of the received baseband signal is calculated by the delay amount and the correlation accumulation window length, and the delay autocorrelation R(τ) of the received signal u is defined as follows: Step 3: R(τ) according to L 1,short is the delay amount, according to L 2,short -1 is the number of accumulations, and the delayed accumulation of the second layer is performed to obtain the final autocorrelation result P(d): Step 4: Calculate the average power E(d) of the received signal. The calculation method is as follows: Step 5: Search for the peak value of the autocorrelation result P(d) within the preset synchronous search window. The peak position is recorded as Where argmax(x) means searching for the maximum value of x; Step 6: After the preset autocorrelation threshold is weighted by the average power of the received signal, it is compared with the searched peak value to obtain the autocorrelation synchronization success indication flag. short : Among them, flag short The value of 1 indicates successful synchronization, and 0 indicates unsuccessful; Step 7, if flag short If flag is equal to 0, it means that no valid MB-OFDM signal has been found and it is necessary to return to step 1 to continue searching. short If it is equal to 1, it means that a valid MB-OFDM signal has been captured, the frequency offset is estimated using the correlation peak, and the estimated frequency offset and peak position are output as the synchronization result. The system state machine enters the long synchronization signal synchronization phase starting from step 8. The frequency offset calculation method is as follows: Among them, arg(x) represents the angle of x; Step 8: Insert the frequency deviation compensation module to compensate the frequency deviation. Adjust the symbol timing, and calculate the boundary position of the long synchronization signal according to the length of the short synchronization signal sequence, and use this to cut out the long synchronization signal from the received signal; Step 9: Receive the long synchronization signal according to L 1,long is the delay amount, L 1,long For the accumulation window, calculate the delay-related value: Detailed estimation results of residual frequency offset Calculated from the phase of the autocorrelation peak: in, represents the autocorrelation peak position; Step 10: A frequency offset compensation module is placed to further compensate for the frequency offset; a cross-correlation operation is performed on the long synchronization signal to obtain accurate symbol timing based on the cross-correlation peak position; The English symbols are defined as follows: L short : Total length of short synchronization signal in MB-OFDM system L 1,short : MB-OFDM system short synchronization signal layer 1 subsequence length L 2,short : MB-OFDM system short synchronization signal layer 2 subsequence length y short :Layer 2 time domain sequence of short synchronization signal in MB-OFDM system y short,k :y short The kth element of L long : The main sequence length of the long synchronization signal in the MB-OFDM system u: baseband received signal of MB-OFDM system R(τ): MB-OFDM system short synchronization signal autocorrelator output P(d): Output of the second-layer unweighted combination of the short synchronization signal autocorrelation of the MB-OFDM system E(d): Average power of received signal in MB-OFDM system The maximum position of P(d) square flag short :MB-OFDM system short synchronization signal synchronization success indication signal Coarse frequency offset estimation results of short synchronization signal in MB-OFDM system f s : Sampling rate of MB-OFDM system R long (d) MB-OFDM system long synchronization signal autocorrelator output R long (d) Maximum position of the square The frequency offset estimation results of the subdivision number of the long synchronization signal in the MB-OFDM system.

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